Heart valve disease is a widespread condition in which one or more of the valves of the heart fails to function properly. Various surgical techniques may be used to replace or repair a diseased or damaged valve. In just one way, in a valve replacement surgery, damaged leaflets of the valve are excised and the annulus is sculpted to receive a replacement valve. Another less drastic method for treating defective valves is repair or reconstruction by annuloplasty, in which the valve annulus is re-shaped and held in place by attaching a prosthetic annuloplasty repair segment or ring to an interior wall of the heart around the valve annulus. The annuloplasty ring is designed to support the functional changes that occur during the cardiac cycle; maintaining coaptation and valve integrity.
There are two atrio-ventricular valves in the heart, which include the mitral valve on the left side of the heart and the tricuspid valve on the right side of the heart. Anatomically speaking, each valve type forms or defines a valve annulus and valve leaflets; however, the mitral and tricuspid valves differ significantly in anatomy. Whereas the annulus of the mitral valve is somewhat “D” shaped, the annulus of the tricuspid valve is more nearly elliptical. Both valves can be subjected to or incur damage that requires that one or both of the valves be repaired or replaced. Annuloplasty prostheses, which can generally be categorized as either annuloplasty rings or annuloplasty bands, are employed in conjunction with valvular reconstructive surgery to assist in the correction of heart valve defects such as stenosis and valvular insufficiency.
One type of valvular insufficiency is ischemic mitral regurgitation (IMR). In IMR, the coordination of the mitral leaflets, the mitral annulus, the subvalvular apparatus and the left ventricular wall is upset in some way. There are many causes, such as congenital defects, rheumatic fever, endocarditis, etc. There is a classification system for IMR, which was developed by Carpentier. IMR is classified as either Type I, II, IIIa or IIIb, based mainly on leaflet motion.
The effects of valvular dysfunction vary, with IMR typically having more severe physiological consequences to the patient than tricuspid valve regurgitation. In either area of the heart, however, many of the defects are associated with dilation of the valve annulus. This dilation not only prevents competence of the valve but also results in distortion of the normal shape of the valve orifice. Remodeling of the annulus is therefore central to most reconstructive procedures on the valves. Clinical experience has shown that repair of the valves, when technically possible, produces better long-term results than valve replacement.
With regard to the mitral valve, many procedures have been described to correct the pathology of the valve leaflets and their associated chordae tendinae and papillary muscles. The mitral valve, in particular, is a bicuspid valve having a posterior leaflet that has an annulus insertion length, that is larger than that of an anterior leaflet, which coapts or meets with the posterior leaflet. Each of the leaflets has indentations dividing them each into three segments, with the posterior leaflet having segments P1 (anterolateral), P2 (middle) and P3 (posteromedial), and the anterior leaflet having segments A1 (anterolateral), A2 (middle) and A3 (posteromedial). The part of the mitral valve annulus that is attached to the anterior leaflet is called the anterior aspect, while the part attached to the posterior leaflet is called the posterior aspect. The two leaflets are fused at two commissures that are inserted in the annulus just below the level of two cardiac trigones, called the anterolateral trigone and the posterolateral trigone.
In mitral valve repair, coaptation of the posterior and anterior leaflets is important. Also, it is considered important to preserve the normal distance between the two trigones. A significant surgical diminution of the inter-trigonal distance may cause left ventricular outflow obstruction and/or distortion of the base of the aortic valve. Thus, it is desirable to maintain the natural inter-trigonal distance and shape following mitral valve repair surgery.
Mitral valve annulus dilation tends to be confined, to the posterior aspect, resulting in a posterior aspect that is larger than normal. Consequently, the repair of mitral valve annulus dilation generally involves reducing the size of the posterior aspect.
In the repair of mitral valve annulus dilation, the associated procedure begins with identification of the trigones. The distance between the trigones (i.e., inter-trigonal distance) or commissures (i.e., inter-commissural distance) remains practically constant during the cardiac cycle in any one particular patient, but may vary from 24 to 40 mm in length in patients. Annuloplasty devices used to treat mitral valve dilation are available in different sizes based upon the distance between the trigones along the anterior aspect (i.e., the aortic curtain). Alternatively, anterior and posterior commissures of the heart are used to size a valve annulus. Either way, it is critical to the successful outcome of the annuloplasty procedure to accurately determine the size of the annulus. Generally, the annuloplasty devices are available in even 2 mm increments from about 24 mm to about 40 mm.
As a part of the mitral valve repair using remodeling, the annulus is generally brought into its shape and positioned such that the inter-trigonal (or inter-commissural) distance is like that at the end of systole. Generally, the involved segment of the annulus, mainly the posterior aspect, is diminished (i.e., constricted) so that the leaflets may coapt correctly on closing, or the annulus is stabilized to prevent post-operative dilatation from occurring. Either result is frequently achieved by the implantation of a prosthetic ring or band in a supra annular position. The purpose of the ring or band is to restrict, remodel and/or support the annulus to correct and/or prevent valvular insufficiency.
Annuloplasty devices for mitral valve repair have generally been configured to restore the original, healthy shape of the mitral annulus at the end of systole. The ring is typically semi-rigid, planar and restores the primary anterior-posterior (A-P) dimension or ratio of the mitral annulus. The ring typically allows for sufficient coaptation of the leaflets at the end of systole.
When annuloplasty devices are used to reduce dilation of the mitral valve and coapt the leaflets, in some cases there is excess leaflet tissue. For example, with Barlow's disease, excess mitral valve leaflet tissue exists. This may result in mitral valve regurgitation. In particular, the anterior mitral leaflet may have excess tissue that, after implantation of the annuloplasty device may experience systolic anterior motion (SAM), which is when the anterior leaflet is pulled into the outflow tract of the left ventricle during the systolic phase of the cardiac cycle. This causes the mitral valve to leak back into the left atrium.
There is a continued desire to be able to improve annuloplasty devices to accommodate different physical structures of the heart due to different disease states of the heart.